UC Santa Barbara

Water pollution with pathogenic microorganisms is a serious threat to human health, particularly in developing countries. Although traditional disinfection technologies, such as the use of chlorine-containing substances, ozone and UV radiation, are effective to control microorganism contamination in water sources, they present some disadvantages such as the generation of disinfection byproducts or high energy consumption, which are major concerns when considering their sustainable use. Thus, this dissertation proposes a novel disinfection system employing metal ions as disinfectants, which can be recovered using magnetic nanoparticles to reuse the disinfecting agents. Various microorganisms, including bacteria, toxic cyanobacteria and waterborne virus are used for case studies to evaluate the efficacy of this novel method, and the reusability of disinfectants and magnetic nanoparticles are explored for long term application.Chapter II presents a sustainable disinfection method with recyclable metal ions and magnetic nanoparticles applied to E. coli K12. The disinfection ability of Ag+, Cu2+ and Zn2+ were evaluated. Ag+ performed best to inactivate E. coli K12, compared to Cu2+ and Zn2+, with minimal effect of the general water characteristics except Cl-. The concentration of residual metal ions was maintained under a safe level, according to EPA guidelines, via sorption by magnetic nanoparticles. Both the magnetic nanoparticles and metal ions can be regenerated and reused with simple operating conditions and high recovery efficiency after 5 continuous cycles, indicating that this method is very promising for practical application. Chapter III optimizes the disinfection method to address toxic cyanobacteria contamination. A combination of metal ions, namely Ag+ and Cu2+, was applied to the disinfection of cyanobacteria. The disinfection effectiveness of the combination was more effective compared to individual Ag+ or Cu2+, especially at low concentration of disinfectants and short contact time. In addition, the results in Chapter III demonstrate that the cyanotoxins produced during disinfection and the residual metal ions can be removed effectively via simultaneous sorption by recyclable magnetic nanoparticles. Chapter IV explores the disinfection of waterborne viruses with magnetic nanoparticles coated by various metal ions, including Ag+, Cu2+ and Fe3+. All three magnetic nanoparticles with metal ions can inactivate above 99% of the target viruses within 0.5 hours, and the magnetic nanoparticles with Cu2+ and Fe3+ are more suitable for large-scale application than with Ag+, considering the price of metal ions. The recovery of the nanoparticles can be easily achieved with external magnetic field, for their regeneration and recycling. The disinfection efficiency remains above 99% after 5 continuous disinfection cycles. This dissertation contributes to overcome some of the disadvantages of traditional disinfection methods in a drinking water treatment plant, providing a novel approach that recovers a large fraction of the disinfectants for reuse. It serves as a scientific reference for environmental engineers in drinking water treatment, by providing an innovative approach for disinfection of water sources contaminated with a range of pathogens.